Why and When to Manage

To achieve sustainable development of the coastal zone it is important to recognise the role played by natural and semi-natural habitats and to maintain and enhance these as part of coastal defence management. Within this, it is important to develop an understanding of the requirements of these habitats and how and when to intervene to enhance them either to provide a coastal defence function or for their biodiversity value.

In the context of the wider estuary environment, saltmarsh maintenance or enhancement is increasingly being considered as a means of providing a long term and more sustainable approach to coastal defence. It also has the added advantage of enhancing the conservation importance of a natural habitat. Initiatives such as those undertaken by the ‘Living with the Sea’ LIFE Nature project address the issues of saltmarsh change. The seven pilot Coastal Habitat Management Plans (CHaMPs) make a key contribution to the development of coastal management policy, providing a better understanding of the impacts of coastal change over the next 30 to 100 years on the habitats and birds of European importance.

The Good Practice Guide to Coastal Habitat Restoration, produced as part of the Living with the Sea project, is a useful information resource for coastal managers. Based on case studies and experience from the UK and overseas, and by linking to other sources of information, it provides a ‘route to restoration’ for eight UK coastal habitats, including saltmarsh. Building on this, and other work, this section of the Saltmarsh Management Manual presents details of a range of techniques that are available for maintaining, restoring or enhancing saltmarshes. It also provides references for saltmarsh creation techniques (realignment and regulated tidal exchange) that can be used in areas where there is no existing saltmarsh. Although these techniques are not strictly related to the management of existing saltmarsh, they are considered here because they represent an important option for the future management of the coast and estuaries in those situations where the existing marsh is significantly threatened by erosive process (refer to saltmarsh classification for further information).

At the broadest level, a scheme to maintain, restore or enhance a saltmarsh should be set within the broader context of an overall management plan for the coastline. Such an overall management approach should involve:

• Gathering data on the present-day status of the saltmarsh and on its recent changes.
• Identifying any problems and their causes (especially those that affect flood defences).
• Assessing the consequences of not intervening (in financial, social and environmental terms).
• Identifying suitable management options and assessing their likely efficiency and costs.
• Further gathering of data to monitor the effectiveness of any scheme.

In general, if the physical processes within an estuary are suitable for saltmarsh formation, the saltmarsh will be self-sustaining. However, saltmarshes can degenerate for a number of reasons, including sea level rise, changes in drainage patterns, disruption to the estuarine processes and changes in land use on or adjacent to the marsh. It is important to understand where such change is the result of a localised impact and where it is part of a wider scale of change. For example, an estuary might change its shape in relation to a change in incident energy but the overall area of saltmarsh in the estuary may remain unchanged.

Where a saltmarsh is suffering from local erosion, some form of active management may be required to alter the environment and to achieve a more appropriate regime. Saltmarsh management in this context largely takes the form of the restoration of degraded marshes, as opposed to regeneration or re-creation (which can involve the establishment of marsh on areas where they have been entirely lost to land claim). Protecting or restoring saltmarshes by preventing erosion or promoting accretion (including seawards of the saltmarsh) is now less favoured, especially in areas where relative sea level is rising (Living with the Sea, 2003). In such circumstances, it may be more appropriate to adopt a strategy which accepts a landward movement of the saltmarsh to a more sustainable position in relation to physical change.

There have been considerable developments in the area of saltmarsh creation over the past two decades (especially in the USA and UK ), as a result of which there are several comprehensive references available relating to creation and regeneration techniques. This section does not, therefore, concentrate on saltmarsh creation or regeneration techniques; rather it concentrates on the management of existing saltmarshes.

As a general rule, management is not required where the saltmarsh remains in a healthy, functioning state and, consequently, can respond and adapt to most changes. Conversely, if change is particularly rapid or (potentially as a result of such change) the saltmarsh has become degraded or is eroding, then a programme of remedial work may be required. In the latter case and if sufficient space is available to allow the saltmarsh to move landwards, then a natural process or roll-over may occur that retains both the flood management and biodiversity value and economic benefits of the saltmarsh. There should be a presumption against interference in the landward retreat of saltmarsh, unless important assets are at risk.

Guidance on the selection of suitable management options is provided to help coastal managers decide whether or not it is appropriate to conduct saltmarsh maintenance and/or enhancement. Considerations include:

• the likely cause of saltmarsh loss or deterioration;
• the rate of loss;
• the cost-benefit of installing and maintaining the scheme; and,
• the potential environmental impact.

Basic guidance on the steps to be undertaken in determining the most appropriate course of management is also provided.

Information on suitable techniques for saltmarsh management (based on a number of different requirements), is provided with appropriate case study examples. The potential environmental effects are discussed and the effectiveness of the various techniques at maintaining and enhancing saltmarsh habitat is reviewed. In broad terms, the financial implications of different management techniques are also considered.

Routine monitoring of saltmarsh is also an important aspect of saltmarsh management. Without it, the first recognition of saltmarsh deterioration could be loss of a habitat or wave damage/increased overtopping to flood embankments and consequent damage to land-based assets. If intervention is left too late, then the damage to the saltmarsh could be too severe to respond with maintenance and enhancement schemes and major intervention may be required. Leaving things too late will also tend to reduce the options for management and to drive the solution towards landward movement of the defence line. Therefore, guidance on monitoring is provided through descriptions of the general components of a saltmarsh monitoring programme, and the various techniques available for monitoring saltmarsh parameters, accompanied by recommendations for monitoring programmes.